﻿#define _CRT_SECURE_NO_WARNINGS 1
class Solution {
public:
    int numDecodings(string s) {
        int n = s.size();

        vector<int> dp(n);
        if (s[0] != '0')
        {
            dp[0] = 1;

        }
        if (n == 1)
        {
            return dp[0];
        }
        if (s[0] != '0' && s[1] != '0')
        {
            dp[1] += 1;
        }
        int t = (s[0] - '0') * 10 + (s[1] - '0');
        if (t >= 10 && t <= 26)
        {
            dp[1] += 1;
        }


        for (int i = 2; i < n; i++)
        {


            if (s[i] <= '9' && s[i] >= '1') dp[i] += dp[i - 1];
            // 如果和前⾯的⼀个数联合起来编码
            int t = (s[i - 1] - '0') * 10 + s[i] - '0';
            if (t >= 10 && t <= 26) dp[i] += dp[i - 2];
        }

        return dp[n - 1];

    }
};